Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D30/00—Field-effect transistors [FET]
  • H10D30/01—Manufacture or treatment
  • H10D30/061—Manufacture or treatment of FETs having Schottky gates
  • H10D30/0612—Manufacture or treatment of FETs having Schottky gates of lateral single-gate Schottky FETs
  • H10D30/0614—Manufacture or treatment of FETs having Schottky gates of lateral single-gate Schottky FETs using processes wherein the final gate is made after the completion of the source and drain regions, e.g. gate-last processes using dummy gates
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S148/00—Metal treatment
  • Y10S148/053—Field effect transistors fets
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S148/00—Metal treatment
  • Y10S148/139—Schottky barrier
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S148/00—Metal treatment
  • Y10S148/14—Schottky barrier contacts

Definitions

• the annealing step in the fabrication of III-V compound semiconductors generally requires a cap to prevent elemental evaporation.
• the fabrication of III-V compound semiconductors generally requires a cap to prevent elemental evaporation.
• caps are generally used to prevent arsine evaporation, thereby maintaining the stoichiometry of the material.
• the transistor is first fabricated up to the
• Ion implantation is then utilized to form highly conductive areas for the source and drain.
• the gate acts as a mask to ' protect certain areas from ion implantation. Consequently, the highly conductive
• 25 source and drain areas extend to a region directly underneath the gate area, thereby reducing source and gate resistance. Thereafter, an annealing cap is deposited and the sample is annealed for r activation of the implanted species. The annealing cap is removed and further fabrication steps are implemented to produce a semiconductor device.
• Circuit performance is dependent upon gate length because the transistor's performance is strongly influenced by gate length. It is highly desirable to have a slightly longer channel 0 length underneath the gate of a semiconductor
• a dummy gate was deposited onto a silicon dioxide layer on top of the channel region of a substrate.
• An aluminum layer was 0 deposited onto the silicon dioxide before etching techniques were utilized to remove portions of the silicon dioxide layer.
• the resultant dummy gate was a structure of a silicon dioxide layer having an aluminum cap deposited thereon.
• the wafer was 5 then ion implanted, utilizing the aluminum cap as a mask to protect the channel from ion implantation.
• Thfc dummy gate was thereafter etched to form an undercut beneath the aluminum mask. This process allows the final gate metal length to be smaller 0 than the channel length because the gate metal is deposited into the space left behind after the dummy gate has been removed.
• the aluminum cap is then stripped off and an annealing cap is applied before high temperature annealing is performed, whereby arsenic evaporation is prevented in gallium arsenide devices.
• This method cannot reliably control the uniformity of the gate length because the undercutting operation cannot be controlled sufficiently.
• the granular size of the aluminum is too large to be suitable for sub-micron geometries because a ragged gate structure is produced.
• the lifting off of the aluminum gate mask after the silicon dioxide annealing cap has been deposited is difficult to achieve by using chemical etching. Because gate length strongly influences a FET's performance, circuit performance is difficult to control if gate length cannot be consistently uniform.
• the IGFET is formed on a gallium arsenide wafer which is coated with a layer of silicon nitride and a silicon dioxide layer.. The silicon dioxide is etched away in transistor areas and ion implanting provides channel doping. A gate of refractory metal such as molybdenum is deposited and delineated. The gate and silicon dioxide act as masks for ion implantation of the source and drain. No dummy or substitutional gates are used to control the gate length.
• a Schottky gate FET is fabricated by forming on a semiconductor substrate first and second stacks facing each other. Each stack is constructed by an ohmic electrode and a spacer film. On the substrate having stacks formed thereon an insulation layer is formed and is anisotropically etched in the direction of its thickness until the planar surface portions are exposed. As a result, portions of the insulation layer remain on opposing sidewalls of the stacks.
• a layer of a metallic material capable of forming a Schottky barrier with the substrate is formed.
• the remaining portions are removed- to pattern the metallic material layer, thereby forming a Schottky gate electrode.
• the present invention provides an im ⁇ proved process for producing a semiconductor device. More specifically, the present invention provides a process utilizing a substitutional gate having sidewall constructions to mask channel regions during ion implantation steps.
• the process comprises depositing a layer of insulator material onto a supporting substrate on its surface.
• the substrate includes a channel region below the surface containing a carrier concentration of a desired conductivity type. Removing selected portions of the insulator mater ⁇ ial forms a substitutional gate on the substrate surface. Sidewalls are formed which bind the substitutional gate to define an effective masking area in cooperation with the substitutional gate. Ion implanting over the masked area places a dopant into the unmasked region of the substrate to provide n+ channel doping in desired areas. The sidewalls are removed and the resultant device is annealed to activate the dopant in the substrate.
• Removing the substitutional gate and depositing gate metal into the space remaining after the gate has been removed controls the gate length because the length will be the same as the substitutional gate, while the channel length will be the same as the substitutional gate plus the sidewalls. It is very desirable to have a channel length longer than the gate length.
• First and second ohmic contacts are deposited in correct positional relation to one another on the substrate, and metallic intercon ⁇ nects are deposited in electrical communication with the ohmic contacts to produce a semiconductor device.
• the supporting substrate preferably includes semi-insulating gallium arsenide but may be other Group III-V compounds or silicon.
• the insulator material may be silicon dioxide, while the sidewalls may be made of silicon nitride, polymers or photoresist. .N or n+-type implantation species are ion implanted while the gate and sidewalls act as a mask to prevent ion implantation directly under the area they are masking. Removing of the sidewalls is accomplished by dry etching or reactive ion etching. To compliment this process, capless annealing may be performed at high tempera- tures, using arsine gas environments in an over ⁇ pressure.
• Planarizing material such as polymers or photoresist is applied as a confor al layer over the substrate surface and the substitutional gate, and is etched back to expose the substitutional gate which is thereafter removed by the application of buffered hydrofluoric acid.
• the planarizing material forms a desired angle between-the top of the planarizing material structure, the bottom of the structure and the surface of the substrate by virtue of the substitutional gate profile. This undercutting defines a certain shape of gate metal when it is deposited into the area left empty by the removal of the substitutional gate.
• the r remaining process steps are standard in the art for the production of a semiconductor device.
• Figure 1 is a side sectional view of a field effect transistor fabricated in accordance 15 with the present invention.
• FIG. 2 illustrates representative steps in the fabrication of the MESFET of the present invention.
• FIG. 1 a field effect transistor 10 fabricated by the present invention is illustrated. As shown, the transistor 10 is formed on a substrate 12 of semiconductor material
• the substrate 12 has a surface 14 and includes a channel region 16 below the surface thereof containing a carrier concentration of a desired conductivity type, such as n, n+, n-, p or p+.
• a gate 22 having a gate length of a controlled dimension to reduce the breakdown voltage at the gate due to the increased separation 16 of the gate from the end of the channels 18.
• Gate 22 is operative to form a channel region 18 proximate the interface with the substrate .12, enabling the transistor 10 to achieve a relatively high transconductance.
• a drain 24 and a source 26 are On top of the substrate 12 .
• the insulator material utilized for the substitutional gate is preferably silicon dioxide or photoresist, or may also be made of a composi ⁇ tion selected from the group consisting of aluminum nitride, aluminum oxide, tantalum oxide, titanium oxide, tungsten oxide, gallium oxide, arsenic oxide, molybdenum oxide, oxynitride, gallium arsenide oxide, aluminum gallium arsenide oxide, indium gallium arsenide phosphide oxide and indium phosphide oxide.
• Gate 22 is generally made of a multi-layered structure consisting of refractory materials, such as platinum and gold. Gate 22 is deposited directly on top of substrate 12. Depo ⁇ ited on the substrate 12 is a drain 24 of ohmic material, acting as the drain electrode. A source 26, also made of an ohmic material, is deposited over the substrate 12 on the opposite side of gate 22 from drain 24. Drain 24 and source 26 may be formed of any suitable ohmic material, such as aluminum, molybdenum or molybdenum tantalum alloy, chrome, titanium, tungsten, palladium and platinum. Preferably, * the ohmic material is gold-germanium.
• the drain 24 and source 26 include an ion implanted region having a carrier conductivity of a desired conductivity type, preferably n+. Both the drain 24 and the source 26 are self-aligned to the gate 22. Metallic interconnects 28 are deposited on top of both said drain 24 and source 26 to act as an electrical connection for current conduction paths in the transistor.
• a region below the surface of a substrate is ion implanted to form a channel containing a carrier concentration of a desired conductivity type and is thereafter annealed at a high temperature, from about 800 to 850° Celsius to activate the ion implanted region.
• a layer of insulator is deposited onto the substrate and selectively etched away to reduce the layer to a substitutional gate. The deposition of the substi- tutional gate insulator material may be accom ⁇ plished by any standard deposition technique.
• sidewalls are formed on the substitutional gate by depositing a conformal layer of ⁇ idewall material, such as a dielectric material which may be selected from the group consisting of silicon dioxide, silicon nitride, polymers and photoresist over the entire substrate and the substitutional gate. Dry etching is then performed to form the sidewalls. Preferentially, reactive ion etching is used because the sidewall material selectively etches away much faster than the substitutional gate material, i.e. something on the order of 20-1 etching rates. The reactive ion etching process
• ion implan- ting is accomplished by ion implanting an n+ type implantation species while the substitutional gate and the sidewalls provide a mask to prevent ion implantation immediately below and adjacent to the substitutional gate;
• the ion implantation process induces a straggling n+ area to slightly encroach into the area under the sidewall construction, providing a channel length which is longer than the substitutional gate length.
• Removing of the sidewalls after ion implantation is accomplished by dry etching. preferably reactive ion etching or plasma etching, leaving the substitutional gate.
• capless annealing is accomplished by placing the structure in an arsine environment overpressure at a high temperature. This annealing is performed from about 750 to 1200° Celsius at an over pressure of arsine from about 0.010 to about 0.10 atmospheric pressure. The annealing may be performed in a composite gas environment containing at least arsi.ne for about 10 seconds to 60 minutes. Preferably, the annealing is performed for about twenty minutes. After annealing, a planarizing material selected from the group consisting of polymers and photoresist is applied as a conformal layer over the substrate surface and the substitu ⁇ tional gate.
• the planarizing material is etched back to expose the substitutional gate. Once the substitutional gate is exposed, buffered hydro ⁇ fluoric acid is applied to the structure to remove the substitutional gate. This forms a planarizing material structure having a desired angle between the top of the structure, the bottom of the struc- ture and the surface of the structure.
• the under ⁇ cutting is performed to form an angle of from about 75° to 90°, but preferably is between 80 and 85°. This undercutting will facilitate gate metal lift-off and also define the shape of the gate material deposited thereafter because the gate metal is deposited into the space left by the substitutional gate and conforms to the undercut planarizing material.
• Depositing of the gate material is accomplished by the deposition of a multi-layer structure including refractory materials, such as platinum and gold, in a conformal fashion atop the entire surface of the substrate.
• planarizing material is then stripped away, taking with it the gate material deposited thereon, leaving the gate metal deposited on top of the substrate.
• Ohmic contacts are then deposited over the region which was left unmasked by the substitutional gate.
• Metallic interconnects are deposited over the ohmic contacts to provide conduction paths for electricity through the transistor. Further conventional techniques are used to complete the transistor for incorporation into semiconductor devices.

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• Junction Field-Effect Transistors (AREA)

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• 1986
  • 1986-06-12 US US06/873,515 patent/US4745082A/en not_active Expired - Fee Related
• 1987
  • 1987-06-10 GB GB8802340A patent/GB2199445B/en not_active Expired
  • 1987-06-10 WO PCT/US1987/001354 patent/WO1987007765A1/en active Application Filing
  • 1987-06-10 JP JP62503800A patent/JPH01500550A/ja active Pending
  • 1987-06-10 DE DE19873790294 patent/DE3790294T1/de not_active Withdrawn
  • 1987-06-11 CA CA000539413A patent/CA1276315C/en not_active Expired - Fee Related

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